The objective of the proposed research is to design, develop, and build a laser specifically for performing laser-assisted vascular anastomoses of small diameter vessels (1-5 mm). The 1.9 um light has optimal absorption characteristics to ensure an even deposition of energy in the walls of small vessels. This would result in a more desirable temperature profile in the region of the anastomosis when compared with alternative sources. The proposed laser has several advantages over the more commonly used CO2 and Ar lasers. Unlike the CO2 laser, the 1.9 um output is transmittable through silica fiber optics, thus facilitating operative convenience and control in the sterile field. Compared to the Ar laser, the 1.9 um laser requires lower power for welding and no irrigation is necessary to prevent tissue damage. Such a source for welding small diameter vessels can have several advantages over manual suturing, some examples of which are shorter operative times, and less foreign body reaction at the anastomosis. Phase I demonstrated the importance of matching the optical penetration depth of the laser radiation to the vessel wall thickness. Anastomoses welded by the 1.9 um laser resulted in the highest burst strength for vessels with wall thickness of about 0.13 mm and diameters of < 1 mm. The fiber optic delivery capability is a significant advantage for this realm of micro- anastomotic repairs. In the Phase II program, emphasis will be placed on (1) better control and understanding of the welding process through temperature/time profiling, (2) development of a compact to permit optimal welding for micro-anastomoses and small vessel anastomoses using a single laser, and (3) chronic studies to determine the safety and efficacy of welds in animals in preparation for the submission of an IDE for clinical trials.